The potential use of long electric conductors in space in a form of electrodynamic tethers was discovered in early 80's. Electrodynamic tethers in space have attracted a lot of attention in recent years. Many researchers have contributed to the theory of their behavior in orbit. Some flight experiments have provided data on the interaction between the electrodynamic tethers and the geomagnetic field and ionosphere.
Typically, an electrodynamic tether is a long electrical conductor that can be used to generate power and/or propulsion as the tether orbits a celestial body with a magnetic field. Flight experiments have provided data on the interaction between electrodynamic tethers and the geomagnetic field and ionosphere of the Earth.
In 1993, the Plasma Motor Generator (PMG) experiment was performed on a Delta rocket with a primary goal of testing power generation and thrust by means of an electrodynamic tether. In the PMG experiment, a 500 meter (m) long electrodynamic tether was deployed into the ionosphere. The tether included a conducting wire with hollow cathodes at each end. An electric current was produced in the tether, demonstrating the potential of this technique to generate power and propulsion that could be used by satellites or space stations in low Earth orbit (LEO). The PMG mission was an example of a propulsion system for space transportation that did not utilize propellant, but rather achieved propulsion by converting orbital energy into electrical energy (deorbit) or electrical energy into orbital energy (orbit boosting).
Two Tethered Satellite System (TSS) missions were flown in 1992 and 1996. The TSS included a satellite, a conducting tether, and a tether deployment/retrieval system flown on the Space Shuttle. Objectives of the TSS missions were to understand the electro-magnetic interaction between the tether system and the ambient space plasma, investigate its dynamics, and demonstrate current collection from the ionosphere to further develop tether capabilities for future tether applications on the Space Shuttle and Space Station. In the TSS-1 mission of 1992, the tether was only partially deployed and the mission was aborted.
The TSS-1R mission of 1996 was a re-flight of the TSS-1 mission. The tether was deployed to the length of 19.7 km when it was severed by an electrical arc. Nevertheless, it was a significant mission for tethered satellites because it showed that electrodynamic tethers were more efficient than theoretically predicted, providing valuable data on electrical performance of the system. Power generation of several kilowatts was demonstrated.
“Tethers in Space Handbook,” Second Edition, NASA Office of Space Flight, NASA Headquarters, Washington, D.C., 1989, edited by P. A. Penzo and P. W. Ammann, provides summaries of various applications and features of electrodynamic tethers, including methods to change orbital elements with electrodynamic tether propulsion and methods to control attitude dynamics of tethers.
Typically, electrodynamic tethers are very long and operate at high voltages. The electrodynamic tethers run the risk of arcing as in the TSS-1R mission. Also, the electrodynamic tethers are susceptible to damage from meteors and/or debris due to the length of the tethers. In addition, electrodynamic tethers are difficult to scale up to move heavy payloads.
For these and other reasons, there is a need for the present invention.